This research constitutes a continuation of our investigation of the factors which determine the stability of the different types of hemoglobins upon subjection to changes in their physiological environment. This is a systematic study designed to elucidate the relative contribution of such intrinsic structural factors as amino acid composition, sequence, prosthetic groups, type and number of covalent and non-covalent bonds and such extrinsic factors as solvent structure, solute(s) type and composition, temperature, pH, dielectric constant, etc. as they determine the three-dimensional structure and the ultimate stability of the protein. Both the single-chain heme-proteins will be studied in conjunction with the different tetrameric hemoglobins, primarily hemoglobins A and S, to establish the magnitude of the forces stabilizing the quaternary structure of mammalian hemoglobins and its subsequent influence on ligand interaction. This laboratory has been engaged in an extensive program to develop techniques capable of detecting subtle structural alterations of the proteins. The techniques developed in this laboratory include (1) urea perturbation technique, (2) comparative dilatometric titration of proteins in aqueous and in denaturing media and (3) dilatometric analysis of globular proteins exposed to a graded range of concentrations of anionic detergents. Recent preliminary studies, with a reducing reagent, indicate a striking difference between the stability of (unoxygenated) hemoglobin A and S in this medium; whereas, the oxygenated forms of hemoglobin S and A do not exhibit this difference. It is projected to optimize this test system and to establish whether this reagent has utility as a diagnostic test for mass screening for hemoglobin S.